[C++][Modules] A module directive may only appear as the first preprocessing tokens in a file (#144233)

This PR is 2nd part of
[P1857R3](https://github.com/llvm/llvm-project/pull/107168)
implementation, and mainly implement the restriction `A module directive
may only appear as the first preprocessing tokens in a file (excluding
the global module fragment.)`:
[cpp.pre](https://eel.is/c++draft/cpp.pre):
```
module-file:
    pp-global-module-fragment[opt] pp-module group[opt] pp-private-module-fragment[opt]
```

We also refine tests use `split-file` instead of conditional macro.

Signed-off-by: yronglin <yronglin777@gmail.com>

4 files changed, 21 insertions, 0 deletions

diff --git a/clang/lib/Lex/Lexer.cpp b/clang/lib/Lex/Lexer.cpp
index 9320045..b61ea3b 100644
--- a/clang/lib/Lex/Lexer.cpp
+++ b/clang/lib/Lex/Lexer.cpp
@@ -174,6 +174,8 @@ void Lexer::InitLexer(const char *BufStart, const char *BufPtr,
   ExtendedTokenMode = 0;
 
   NewLinePtr = nullptr;
+
+  IsFirstPPToken = true;
 }
 
 /// Lexer constructor - Create a new lexer object for the specified buffer
@@ -3725,6 +3727,11 @@ bool Lexer::Lex(Token &Result) {
     HasLeadingEmptyMacro = false;
   }
 
+  if (IsFirstPPToken) {
+    Result.setFlag(Token::FirstPPToken);
+    IsFirstPPToken = false;
+  }
+
   bool atPhysicalStartOfLine = IsAtPhysicalStartOfLine;
   IsAtPhysicalStartOfLine = false;
   bool isRawLex = isLexingRawMode();
@@ -3732,6 +3739,10 @@ bool Lexer::Lex(Token &Result) {
   bool returnedToken = LexTokenInternal(Result, atPhysicalStartOfLine);
   // (After the LexTokenInternal call, the lexer might be destroyed.)
   assert((returnedToken || !isRawLex) && "Raw lex must succeed");
+
+  if (returnedToken && Result.isFirstPPToken() && PP &&
+      !PP->hasSeenMainFileFirstPPToken())
+    PP->HandleMainFileFirstPPToken(Result);
   return returnedToken;
 }
 
@@ -4535,6 +4546,8 @@ const char *Lexer::convertDependencyDirectiveToken(
   Result.setFlag((Token::TokenFlags)DDTok.Flags);
   Result.setLength(DDTok.Length);
   BufferPtr = TokPtr + DDTok.Length;
+  if (PP && !PP->hasSeenMainFileFirstPPToken() && Result.isFirstPPToken())
+    PP->HandleMainFileFirstPPToken(Result);
   return TokPtr;
 }
 
diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
index 04a30f6..70934b9 100644
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -1242,6 +1242,9 @@ void Preprocessor::HandleDirective(Token &Result) {
   // pp-directive.
   bool ReadAnyTokensBeforeDirective =CurPPLexer->MIOpt.getHasReadAnyTokensVal();
 
+  if (!hasSeenMainFileFirstPPToken())
+    HandleMainFileFirstPPToken(Result);
+
   // Save the '#' token in case we need to return it later.
   Token SavedHash = Result;
 
diff --git a/clang/lib/Lex/PPMacroExpansion.cpp b/clang/lib/Lex/PPMacroExpansion.cpp
index 37ac1bf..97bdeb8 100644
--- a/clang/lib/Lex/PPMacroExpansion.cpp
+++ b/clang/lib/Lex/PPMacroExpansion.cpp
@@ -469,6 +469,9 @@ bool Preprocessor::HandleMacroExpandedIdentifier(Token &Identifier,
   // to disable the optimization in this case.
   if (CurPPLexer) CurPPLexer->MIOpt.ExpandedMacro();
 
+  if (!hasSeenMainFileFirstPPToken())
+    HandleMainFileFirstPPToken(Identifier);
+
   // If this is a builtin macro, like __LINE__ or _Pragma, handle it specially.
   if (MI->isBuiltinMacro()) {
     if (Callbacks)
diff --git a/clang/lib/Lex/Preprocessor.cpp b/clang/lib/Lex/Preprocessor.cpp
index 21fc7a2..18b2f5f 100644
--- a/clang/lib/Lex/Preprocessor.cpp
+++ b/clang/lib/Lex/Preprocessor.cpp
@@ -247,6 +247,8 @@ void Preprocessor::DumpToken(const Token &Tok, bool DumpFlags) const {
     llvm::errs() << " [LeadingSpace]";
   if (Tok.isExpandDisabled())
     llvm::errs() << " [ExpandDisabled]";
+  if (Tok.isFirstPPToken())
+    llvm::errs() << " [First pp-token]";
   if (Tok.needsCleaning()) {
     const char *Start = SourceMgr.getCharacterData(Tok.getLocation());
     llvm::errs() << " [UnClean='" << StringRef(Start, Tok.getLength())